In many laser processing applications, the intensity of a polarized laser beam is varied (e.g., attenuated) using an optical attenuator. In one conventional approach, a combination of a rotating waveplate (or an electro-optic modulator (EOM)) and a subsequent polarizer are used to produce a polarized laser beam having a variable intensity. For example, in a system using a rotating waveplate and subsequent polarizer, the rotating waveplate and subsequent polarizer are positioned in a beam path of a laser beam, and the rotating waveplate is rotated about an axis parallel to the beam path to rotate a polarization vector, which changes the intensity of a polarized laser beam exiting the subsequent polarizer. In another conventional approach, an acousto-optic modulator (AOM) is utilized to produce a polarized laser beam having a variable intensity. In a system using an AOM, an acousto-electric transducer (e.g., a piezo-electric transducer) changes the intensity of a sound wave created in a medium (e.g., glass, quartz) to thereby vary the intensity of a laser beam incident on and diffracted by the medium.
Conventional approaches have a number of shortcomings. For example, an optical attenuator including a rotating waveplate and a subsequent polarizer is relatively slow at varying beam intensity. Although an AOM can quickly vary beam intensity (in about 100 nanoseconds or less), a system implementing an AOM is typically complex, optical alignment of the system is relatively challenging, and the beam path is relatively long. Moreover, an AOM typically has a peak diffraction efficiency below 90% (e.g., about 85%).
What is needed is a system that can quickly vary the intensity of a laser beam, is characterized by optical simplicity, and has a relatively high peak transmission efficiency.